Amplifier with double rail output

ABSTRACT

An amplifier with double rail output being a switchable to single rail output is provided by power pumping circuitry which is controllable by an error detector to deliver modulated power pulses from a d.c. power source to on-following current steering circuits for coupling to either or both of first and second output terminals. In one embodiment the amplifier is envisaged in an integrated circuit form wherein the current steering circuits are provided by switched voltage multipliers of novel structure so that voltage stress of some capacitive elements is reduced, thereby reducing the area these elements would otherwise occupy in the integrated circuit.

This is a division of application Ser. No. 878,729, filed June 26, 1986,now U.S. Pat. No. 4,691,271.

FIELD OF THE INVENTION

The invention relates to apparatus and method for providing a single ordouble railed output signal having either or both of alternating anddirect current components and more particularly relates to supplyinghigh level signals, for example telephone ringing signals, to acommunication line.

BACKGROUND OF THE INVENTION

In a telephone system, ringing signals are usually required to actuate aringer in a called telephone set, thereby giving audible indication of atelephone call. A typical ringing signal consists of a d.c. potential ofbetween 45 and 55 volts and an a.c. potential of between 80 and 120volts RMS being superimposed thereon. The a.c. potential may have afrequency of about 20 Hz which is typical, but frequency divisionmultiplex ringing may require different frequencies in a range of 15 Hzand 100 Hz. In the past it was common for ringers in telephone sets tobe connected between either of tip and ring subscriber loop conductorsand ground to distinguish tip and ring parties. However recently,private line telephone service is increasingly popular and in the caseof private line telephone service the ringer is usually connected acrossthe tip and ring leads. In at least one operating telephone company,ringing signals are supplied from a floating ringing battery source,that is without any reference to ground.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a double rail source of highlevel telephone signals, which is operable from a typical talkingbattery or the like in response to a reference signal.

In accordance with the invention an amplification means includes firstand second outputs for providing an amplified replica of the referencesignal and a complement of same, power terminals for connection to ad.c. power source, and an input. A network includes a first resistorbeing connected between the first output terminal and the input, asecond resistor being connected between the second output terminal andthe input, an inverter connected in series between one of the outputsand the respective resistor, and a third resistor being connectedbetween a reference signal terminal, for receiving the reference signal,and the input of the amplification means.

In an embodiment of the invention, an amplification means includes areference terminal and first and second output terminals. An errordetector is responsive to signals applied to the reference terminal forgenerating a bipolar error signal. A power pumping circuit is connectedbetween the first and second power terminals and includes an output forproviding modulated current pulses in response to an absolute amplitudevalue of the error signal. First and second current steering circuitsare capacitively coupled to the output of the power pumping circuit andare responsive to the modulated current pulses and the polarity of theerror signal for steering currents to and from the respective ones ofthe first and second output terminals.

Each current steering circuit includes a pair of switched voltagemultipliers being polled opposite one with respect to the other. In oneembodiment, the structure of each voltage multiplier is modified withrespect to the classical Cockroft and Walton voltage multiplier suchthat capacitance elements and switch elements are subjected to lesserelectrical stress under some operating conditions than would otherwisebe so.

A voltage multiplier, in accordance with this aspect of the invention,receives electrical energy at an input terminal and provides directcurrent at an output terminal. The voltage multiplier includes aplurality of n unidirectional current conductive elements beingconnected in series between ground and the output terminal and beingpolled in one and the same direction and defining n-1 interconnectingjunctions and an n^(th) junction with the output terminal, wherein n isan even number of at least four. A capacitor element is connectedbetween an alternating current ground and each even numbered one of saidjunctions. A capacitor element is connected between each pair ofconsecutively odd numbered ones of said junctions. An input capacitor isconnected between the input terminal and the n-1 junction.

In another embodiment of the invention the amplifier is switchable tooperate in one of three operating output modes being a differentialoutput mode, a ring ground output mode and a tip ground output mode.

A method in accordance with the invention for supplying high leveltelephone signals to a load being connected via tip and ring terminalsand a communication line, includes the steps of providing a directcurrent power source, and providing a reference signal which defines aparticular high level telephone signal. An error signal is continuouslygenerated by a weighted algebraic summation of the reference signal andsignals at the tip and ring terminals. Electrical energy is stored in aninductor by a momentary conduction of current from the direct currentpower source, the current so conducted being of a magnitude which isdependent upon an absolute value of the error signal. Thereafterelectrical energy is released from the inductor. The released electricalenergy is steered in either of two directions, in accordance with apolarity of the error signal, through the load via the tip and ringterminals and the communciation line. The step of storing and releasingis repeated rapidly in response to a clock signal.

BRIEF DESCRIPTION OF THE DRAWING

An example embodiment is discussed with reference to the accompanyingdrawing which is a schematic diagram illustrating an amplifier inaccordance with the invention for providing high level signals includingringing signals in a telephone system.

DETAILED DESCRIPTION

The amplifier in the drawing includes a double railed output, beingleads 2a and 3a which are coupled through switches 93, 94, 95 and 96 tocorresponding output terminals 2 and 3. Ground connections are indicatedfor connection to a positive terminal of a battery supply, not shown,and a negative supply (-B) terminal 9 is indicated for connection to anegative terminal of the battery supply. Alternating current groundconnections via capacitors 6 and 7 are also indicated for connection toany low impedance in relation to the battery supply. In this examplewherein the use intended for the amplifier is that of a high levelsignal source for a telephone line it is preferred that the a.c. groundsbe connected along with the terminal 9 to the negative terminal of thebattery supply. Differential amplifiers 15 and 17 connected as shownprovide an input for the amplifier whereby an error signal is producedon a lead 16 and its complement is produced on the lead 18. The errorsignal is derived across a network which includes a resistor 11connected between the output lead 2a and an inverting input of theamplifier 15, a unity-gain inverter 14 and a resistor 12 connectedbetween the output lead 3a and the inverting input, and a resistor 13connected between a reference signal terminal 4 and the inverting input.

In operation of the circuit as thus far described, the setting of theswitches 93-96 determines which of the output terminals 2 and 3 isgrounded or if neither is grounded. The potentials at the outputterminals 2 and 3 are applied to the resistor network along with thepotential of a reference signal at the terminal 4 such that an invertedalgebraic summation of these potentials, that is the error signal,appears at the output 16 of the differential amplifier 15. The remainderof the circuitry, which is discussed in more detail in the following,responds to the error signal by adjusting the potential or potentials atthe output terminals 2 or 3, or 2 and 3, as the case may be, to maintaina predetermined operating ratio beween the reference signal and theerror signal.

More specifically, the error signal is used by a regulation portion ofthe amplifier to supply an amount of electrical energy to a load, notshown, connected across the output terminals 2 and 3. The error signaland its complement are used by steering portions of the amplifier at 50aand 50b to determine the polarity of the electrical energy supplied tothe load, and in this example to also amplify or multiply the voltage ofthe electrical energy supplied from the regulation portion of theamplifier.

The regulation portion of the amplifier includes an absolute valuecircuit 19, which generates a rectified error signal at an output 20 inresponse to the error signal on the lead 16. A pulse width modulation(PWM) circuit includes a transistor 22, which is supplied with collectorcurrent from the output 20 via a resistor 21. Clock pulses, in thisexample at a frequency of about 2.5 MHz, are supplied from a source, notshown, to the base of the transistor 22 via a clock terminal 5 and acapacitor 25. A diode 23 and a resistor 24, connected as shown, act toprovide a preferred operating bias at the base of the transistor 22 inthe presence of the clock pulses. During moments when the transistor 22is OFF, a capacitor 26 is charged via the resistor 21 such that thecollector voltage rises toward the potential of the rectified errorsignal. The more positive the error signal voltage becomes, the furtherthe voltage at the collector rises. Each time the transistor 22 isswitched ON, by a positive going portion of the clock pulses at theterminal 5, the capacitor 26 is rapidly discharged with the collectorvoltage dropping rapidly to less than a volt. This results in a periodicsaw tooth-like voltage wave form having a peak amplitude porportional tothe voltage of the rectified error signal. Diodes 27 and 28, a resistor29 and NAND gates 30 and 31, connected as shown, are responsive to thesaw tooth-like voltage waveform at the collector of the transistor 22 togenerate a rectangular or binary-like waveform for driving anon-following power pulse generator (PULSER). At any one instant one ofthe NAND gates 30, 31 is ON and the other is OFF and vice versa. A d.c.bias voltage (V BIAS) supplied at a junction of the cathodes of thediodes 27 and 28 determines a transition potential along the sawtooth-like waveform at which the states of the NAND gates 30 and 31change. In this example, the NAND gates 30 and 31 are supplied withenergizing current from a power source of about 15 volts potential toprovide adequate voltage at the output of the NAND gate 31 to drive thePULSER.

The PULSER includes a switch provided by a field effect transistor (FET)36, a capacitor 32 connected between a gate electrode of the FET 36 andan output of NAND gate 31. Zener diodes 33 and a resistor 34 providebias such that the FET 36 is maintained in an ON state at times when theoutput of the NAND gate 31 is pulsed positive and otherwise ismaintained OFF. The FET 36 while in the ON state conducts currentbetween ground and the negative supply (-B) terminal 9 via an energystorage element which limits the current flow, in this example aninductor 8. As is well known by persons skilled in electrical arts, suchconduction causes magnetic energy to be stored in association with theinductor 8. When the FET 36 is turned OFF, the magnetic energy isreleased in the form of an electrical current, to the steering circuitportions 50a and 50b of the amplifier via a diode 37 connected in serieswith a lead 42. In this example the inductance value of the inductor 8is about 150 microhenries. Diodes 38 and 41 and inductors 39 and 40connected as shown, are not essential but provide a smoothing functionwhich reduces generation of radio frequency interference. The inductancevalue of the inductors 39 and 40 are between 1/15 and 1/30 of theinductance value of the inductor 8.

The steering circuit portion of the amplifier includes a pair of currentsteering circuits 50a and 50b which are responsive to polarities of theerror signal from the differential amplifier 15 and the inverted errorsignal from the differential amplifier 17, to the amplitude of therectified error signal from the absolute value circuit 19, and to switchsettings of switches 91 and 92, for their operation. For simplicity ofillustration only the structure of the steering circuit 50a is shown indetail, as the structure of the steering circuit 50b is identical. Thecurrent steering circuit includes voltage doubler circuits 70 and 80which are polled opposite one with respect to the other. A switchingcircuit including diodes 52-55 and transistors 56 and 57 whichselectively provide ground at an anode of a diode 71 to enable operationof the voltage doubler circuit 70. Likewise a switching circuitincluding diodes 62-65 and transistors 66 and 67 which selectivelyprovide ground at a cathode of a diode 81 to enable operation of thevoltage doubler circuit 80. A resistor 16a is connected between theoutput lead 16 and the diodes 53 and 63. A resistor 18a is connectedbetween the output lead 16 and the diodes 53 and 63. A resistor 18a isconnected between the output lead 18 and the diodes 55 and 65. Aresistor 20a is connected between the reference signal terminal 4 andthe diodes 54 and 64. A resistor 51 is connected between the diode 52and the switch 91 as shown. A resistor 61 is connected between the diode62 and the switch 92 as shown. The switches 91 and 92 are connected toprovide negative, positive or open biases for operation of the diodelogic of the switching circuits and include switching members which areoperable together with switching members of the switches 93-96, asillustrated by a dotted line indicating mechanical linkage therebetween.Each of the switch devices is illustrated as a mechanical apparatus forsimplicity of illustration. It will of course be understood by thoseskilled in this art that the switch devices are conveniently providableby solid state semiconductor circuits each logically coupled with astorage means for retaining the required state of each switch device, asfor example would be a typical arrangement in an integrated circuitembodiment of the invention. In such an integrated circuit embodimentthe inductors 8, 39 and 40 are provided by discrete devices.

In operation, the switches are set for any one of three operationalconfigurations. For example, in one extreme setting the configurationillustrated, the terminal 2 is grounded and the terminal 3 is active.Thus a load when connected between the terminals 2 and 3 is driven orsupplied with regulated electrical energy via the steering circuit 50b.In another extreme setting the load is supplied from the steeringcircuit 50a. In a setting intermediate of the two extreme settings theload is differentially supplied via both the steering circuits 50a and50b in a double railed output configuration with neither of theterminals 2 or 3 being grounded.

In one application of the amplifier in FIG. 1, it is intended for use asa telephone ringing signal generator, capable of supplying up to fivetelephone sets simultaneously with ringing signals via tip and ringleads of a telephone line being connected across the terminals 2 and 3.It is envisaged that in this application the ringing generator is merelyone portion of a semiconductor chip integrated circuit which includes aTDM access system, codec, filter, electronic hybrids, talking batteryline feed and supervisory circuits. Some of the more space consumingelements in such an integrated circuit are the capacitor elements in thevoltage doublers 70 and 80, particularly if the classical Cockroft andWalton voltage multipliers are used.

In the example embodiment a novel voltage multiplier configurationprovides the required voltage doublers. A capacitor 58 is connectedbetween the output of the PULSER and a junction 78 of diodes 74 and 73.A capacitor 75 is connected between the junction 78 and a junction 77 ofdiodes 71 and 72. A capacitor 76 is connected between a.c. ground and ajunction 79 of the diodes 72 and 73. In the voltage doubler 80 acapacitor 68 is connected between the output of the PULSER and ajunction 88 of diodes 83 and 84. A capacitor 85 is connected between thejunction 88 and a junction 87 of the diodes 81 and 82. A capacitor 86 isconnected between a.c. ground and a junction 89 of the diodes 82 and 83.The indicated a.c. grounds are connected to the negative supply terminal9. Electrical energy from the PULSER is coupled to the voltage doublercircuits 70 and 80 by capacitors 58 and 68 respectively. In thisconfiguration voltage stress across the individual capacitor dielectricsis reduced such that the required capacitance is obtainable in a lesserarea of chip geography than would otherwise be the case. A secondadvantage accrues in that the transistors 57 and 67 used with thisconfiguration of voltage multiplier are less severely voltage stressedin the OFF state than would otherwise be the case. Hence the integratedcircuit manufacturing process may be advantageously simplified in viewof the lesser voltage breakdown requirements of these switches.

What is claimed is:
 1. An amplifier for amplifying a reference signal toprovide therefrom at least one of an amplified replica of the referencesignal and its complement comprising:a reference signal terminal forapplication of the reference signal thereto; amplification meansincluding first and second outputs for supplying at least one of theamplified replica and its complement respectively, first and secondpower terminals for connection to a d.c. power source, and an input; anetwork including a first resistor being connected between the firstoutput and the input, a second resistor being connected between thesecond output and the input, and a third resistor being connectedbetween the reference signal terminal and the input; and a unity gaininverter being connected in series with one of the first and secondoutputs and a respective one of the first and second resistors.
 2. Anamplifier as defined in claim 1 wherein the amplification meanscomprises:an error detector being responsive to signals at the referencesignal terminal and at least one of the first and second outputterminals for generating a bipolar error signal; power pumping meansbeing connected between the first and second power terminals and havingan output for providing modulated current pulses in response to anabsolute amplitude value of the error signal; and first and secondcurrent steering means having outputs corresponding to the first andsecond outputs respectively, each current steering means beingcapacitively coupled to the output of the power pumping means and beingresponsive to the modulated current pulses and the polarity of the errorsignal for steering currents to and from the respective output.
 3. Anamplifier as defined in claim 2 wherein the power pumping meanscomprises:an absolute value circuit for generating the absoluteamplitude value in response to the bipolar error signal; and a pulsermeans for generating current pulses of modulated magnitudes in responseto the absolute amplitude value.
 4. An amplifier as defined in claim 3wherein the first current steering means comprises:a first switchedrectifier circuit including a first rectifier being polled to rectifypositive, a second rectifier being polled to rectify negative voltageand a switching circuit for activating one or the other of the first andsecond rectifiers in accordance with the bipolar error signal beingnegative or positive; inputs of the first and second rectifiers beingcapacitively coupled to receive current pulses from the pulser means andoutputs of said rectifiers being connected to a first output terminal;and wherein the second steering circuit comprises: a second switchedrectifier circuit including a first rectifier being polled to rectifypositive voltage, a second rectifier being polled to rectify negativevoltage, and a switching circuit for activating one and the other of thefirst and second rectifiers in accordance with the bipolar error signalbeing positive or negative; inputs of the first and second rectifiersbeing capacitively coupled to receive current pulses from the pulsemeans and outputs of said rectifiers being connected to a second outputterminal.
 5. An amplifier as defined in claim 4 wherein each of theswitched rectifiers comprises:a plurality of n unidirectional currentconductive elements being connected in series between ground and theoutput terminal and being polled in one and the same direction anddefining n-1 interconnecting junctions and an n^(th) junction with theoutput terminal wherein n is an even number of at least four; acapacitor element being connected between an alternative current groundand each even numbered ones of said junctions; a capacitor element beingconnected between each pair of consecutively odd-numbered ones of saidjunctions; an input capacitor element being connected between the inputterminal and the n-1 junction; and a switch means being connectedbetween ground and the n-(n-1) unidirectional conductive element.
 6. Anamplifier as defined in claim 4 and further comprising a switch devicebeing settable to each of three settings for grounding the output of oneor the other of the first and second outputs or neither of the first andsecond outputs respectively and for providing a logic signal indicativeof the instant setting, each of said switched rectifiers beingresponsive to the logic signal from the switch device to be switched OFFwhile its respective output is being grounded by the switch device. 7.An amplifier as defined in claim 5 and further comprising a switchdevice being settable to each of three settings for grounding the outputof one or the other of the first and second outputs or neither of thefirst and second outputs respectively and for providing a logic signalindicative of the instant setting, each of said switched rectifiersbeing responsive to the logic signal from the switch device to beswitched OFF while its respective output is being grounded by the switchdevice.
 8. A method of operating an amplifier connected to a directcurrent power source and also connected to a load via tip and ringterminals, the method comprising the steps of:(a) providing a referencesignal and a clock signal; (b) continuously generating an error signalin response to a weighted algebraic summation of the reference signaland signals at the tip and ring terminals; (c) inductively storingelectrical energy in proportion to absolute value of the error signal atan instant of a pulse of said clock signal; (d) releasing the electricalenergy having been stored in step (c) and steering said released energyto the load via one of said tip and ring terminals in accordance with apolarity of ther error signal at the instant of said pulse; and (e)repeating the steps (c) and (d) at a pulse repetition rate of the clocksignal.